The invention pertains to a process for detecting the state of a catalyst system in an exhaust gas channel of an internal combustion engine of a motor vehicle.
It is known that catalysts, especially so-called 3-way catalysts, can be placed in the exhaust gas channel to purify the exhaust gas of the internal combustion engine. When an air-fuel mixture undergoes combustion, pollutants such as soot particles, nitrogen oxides (NOx), carbon monoxide (CO), and incompletely burned hydrocarbons (HCs) are formed in varying proportions. Reducing agents, i.e., CO, HCs, and H2, are oxidized on the catalysts with oxygen and/or nitrogen oxides to form water and carbon dioxide. Oxidizing agents such as NOx, however, are reduced on the catalysts with the help of reducing agents to form nitrogen.
It is also known that sensors can be assigned to a catalyst system of this type to detect, for example, the percentage of a certain gas component in the exhaust gas (lambda probes, NOx sensors) or to measure a temperature (temperature sensors). The way in which such sensors function and their location in the catalyst system are known.
During the dynamic operation of an internal combustion engine, the conversion rate for the pollutants deteriorates over the course of time as a result of reversible and irreversible damage to the catalysts. It is therefore known that sensors can be used to detect the degree of damage to the catalyst system, in that, for example, an NOx emission downstream of the catalyst system is compared with an NOx emission upstream of the catalyst system. To correct reversible damage, appropriate countermeasures are then usually initiated such as the regeneration of the catalyst in a reductive atmosphere. When the irreversible damage exceeds a predetermined threshold, it will be necessary under certain conditions to perform expensive maintenance work.
The disadvantage of the known processes is that, during the dynamic operation of the internal combustion engine, especially during acceleration phases, the variables on which the detection of the state of the catalyst system is based fluctuate widely. Thus, during periods of high engine power demand, the NOx emissions also increase. Thereafter, it is possible for the threshold values for the degree of damage to the catalyst system to be exceeded briefly, even though such severe damage is not actually present. As a result of this incorrect diagnosis, it is possible under certain conditions for unnecessary regeneration or maintenance procedures to be initiated.